The present invention relates to a process to prepare a cyclic polyester oligomer composition comprising a cyclic polyester oligomer having furanic units, as well as said cyclic polyester oligomer composition obtainable by said process and the use of said cyclic polyester oligomer composition in the production of a polyester polymer.
Polyesters are an important class of commercial polymers with useful physical and mechanical properties and numerous applications. Polyesters find wide utility, for example, as fibres, coatings, films, or in composites. Most industrial polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyacrylates are produced from monomers derived from petrochemical feedstocks. Due to limited oil reserves, fluctuations of oil price, political instability in some production areas, and increased environmental awareness, there is growing interest for biobased polyesters produced from renewable feedstocks.
Currently, there are only few biobased polyesters in commercial or pilot production. Representative examples of naturally-occurring polyesters are polyhydroxyalkanoates (PHA), which are linear polyesters produced by microbial fermentation from sugars or lipids. However PHA has not been widely industrialized due to limitations in production yields and downstream processing.
Another example of an commercially-produced biobased semisynthetic polyester is polylactic acid (PLA), which may be prepared from polycondensation of lactic acid or ring-opening polymerization of the cyclic diester lactide. Although PLA has a wide range of applications, it is an aliphatic polyester and therefore not suitable for replacing petrochemical-based aromatic polyesters in applications such as higher temperature extrusion or molding or the production of bottles. Since most biobased building blocks are derived from non-aromatic compounds such as sugars or starch, most biobased polymers suffer this disadvantage. Examples of other such aliphatic biobased polymers include polybutylene succinate (PBS) or polymers based on sebacic or adipic acids.
For these reasons, biobased polymers having aromatic building blocks are highly sought today. An interesting class of biobased aromatic monomers are the furanics such as furan-2,5-dicarboxylic acid (FDA), 5-(hydroxymethyl)furan-2-carboxylic acid (HMFA), and 2,5-bis(hydroxyl methyl)furan (BHMF), which may be prepared from the intermediates furfural (2-furan carboxaldehyde) and 5-hydroxymethyl 2-furan carboxaldehyde (HMF) which may be produced by the acid-catalyzed thermal dehydration of pentoses (C5) and hexoses (C6). The chemical similarity of the furan ring to the phenyl ring makes it possible to replace phenyl-based polymers such as polyethylene terephthalate (PET) by furan-based polymers.
The production of polyesters from furanic building blocks by polycondensation reactions involving heating a mixture of diols and diacids or diesters (monomers) at high temperatures in the presence of organometallic or acid catalyst is known, for example, from U.S. Pat. No. 2,551,731 and U.S. Pat. No. 8,143,355 B2. To allow the progress in this equilibrium reaction towards the formation of the polymer, the formed water or side products such as alcohol must be removed, typically by reduced pressure or gas streams at elevated temperatures in the process. Therefore complex and costly reaction and devolatilization equipments effective at driving the reaction to completion, devolatilizing significant amounts of volatile compounds from highly viscous polymer melts, and having the capacity to remove and condense these volatile compounds are required. If the polycondensation and devolatilization is insufficient, then high molecular weight polyester having useful mechanical and other properties will not be produced.
Furthermore the high temperatures and long residence times used for (i) driving the polymerization of these diol and diacid or diester monomers and (ii) devolatilization of the resulting polymer lead often to undesired side reactions such as degradation of the monomer, oligomer or polymer, formation of intermolecular bonds leading to branching, and oxidation of the final product with the consequent color development. In addition, significant amounts of volatile organic compounds such as alcoholic side products cannot simply be emitted to the atmosphere, and they must be instead recovered for recycling to make new monomer or for thermal recycling. This recovery and recycling to make new monomer entails costly storage and transport aspects unless the polymerization plant is integrated with an on-site monomer production plant.
In conclusion, it would be desirable to have alternative raw materials to the diol and diacid or diester monomers conventionally used to prepare polyesters from furanic building blocks in industrial scale polymerization plants. Particularly desirable are ones that do not produce large quantities of water or alcoholic side products. Such alternative raw materials would then not require complex reaction and high-capacity devolatilization equipment or harsh high temperature reaction and devolatization steps to drive the polymerization to completion. Therefore such alternative raw materials would allow high molecular weight polymers having furanic units to be readily produced from furanic building blocks under mild conditions.